Heat control device

ABSTRACT

A small size, light weight heat control device feasible for an artificial satellite or a spacecraft is disclosed. The heat control device uses an optical property particular to a substance itself in place of a mechanical principle applied to a conventional thermal louver. In addition, the device of the present invention is highly reliable and long life because it needs no movable portions which would bring about wear, fatigue and other problems.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a heat control device and moreparticularly to a heat control device feasible for, e.g., an artificialsatellite or a spacecraft.

[0002] As for a spacecraft expected to navigate a vacuum environment,heat radiation from outside surfaces is the only heat radiating meansavailable. The amount of heat radiation dictates the temperature insidethe spacecraft. A thermal louver has customarily been used formaintaining temperature inside the spacecraft adequate. The thermallouver adjusts the amount of heat radiation to the outside in accordancewith temperature. Specifically, the louver includes a bimetal or similaractuator for driving blades. The blades are movable to increase ordecrease the effective area and therefore the temperature of heatradiation surfaces, i.e., increase the amount of heat radiation at ahigh temperature or reduces it at a low temperature.

[0003] However, the above thermal louver is a mechanical deviceincluding movable portions and therefore bulky and heavy. Moreover, thelouver lacks in reliability due to the movable portions. In addition,the blades cannot be opened and closed more than a preselected number oftimes due to their limited life.

[0004] Technologies relating to the present invention are also disclosedin, e.g., Japanese Patent Laid-Open Publication Nos, 63-207799, 1-212699and 9-58600.

SUMMARY OF THE INVENTION

[0005] It is therefore an object of the present invention to provide areliable heat control device operable over a long period of time even ina severe environment and easy to produce.

[0006] It is another object of the present invention to provide areliable, small size and light weight heat control device including nomovable portions.

[0007] In a heat control device of the present invention, avariable-phase substance exhibiting a property of an insulator or aproperty of metal in a high temperature phase or a low temperaturephase, respectively, and radiating a great amount of heat or a smallamount of heat in the low temperature phase or the high temperaturephase, respectively, controls the temperature of a desired object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription taken with the accompanying drawings in which:

[0009]FIG. 1 shows a conventional thermal louver:

[0010]FIG. 2 is a graph showing a reflection spectrum particular to avariable-phase substance La_(1-X)Sr_(X)MnO₃ applicable to the presentinvention;

[0011]FIG. 3 is a graph showing resistivity

[0012]FIG. 4 is a graph showing data representative of the reflectivityof La_(1-X)Sr_(X)MnO₃; and

[0013]FIGS. 5 and 6 respectively show a first and a second embodiment ofthe heat control device in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] To better understand the present invention, brief reference willbe made to a conventional thermal louver, shown in FIG. 1. The thermallouver to be described adjusts the amount of heat radiation to theoutside in accordance with temperature, as stated earlier. As shown, thethermal louver includes a bimetal or actuator 10 and blades 12 Thebimetal 10 drives the blade 12 in order to increases or decreases theeffective area and therefore the temperature of heat radiation surfaces.There are also shown in FIG. 1 a frame 14, a bimetal housing 16, shafts18, and bearings 20.

[0015] A heat control device in accordance with the present invention ischaracterized in that it uses a heat radiation characteristic particularto a substance itself in place of a mechanical principle. As for aspacecraft expected to navigate a vacuum environment, heat radiationfrom outside surfaces is the only heat radiating means available. Theamount of heat radiation dictates the temperature inside the spacecraft.

[0016] The heat control device of the present invention is implementedby a variable-phase substance (La_(1-X)Sr_(X)MnO₃) arranged on the heatradiation surfaces of a spacecraft. The variable-phase substance belongsto a family of oxides of perovskite Mn and undergoes phase transitionaround room temperature. The characteristic of this kind of substance issimilar to the characteristic of metal in a low temperature phase, butsimilar to the characteristic of an insulator in a high temperaturephase. Also, the heat radiation ratio of the substance is low whenconductivity is high, but high when conductivity is low. The substancetherefore has an automatic temperature adjusting ability, i.e.,automatically increases its heat radiation ratio at high temperaturesand decreases it at low temperatures. FIG. 1 shows the dependency of theresistivity and infrared reflectivity of La_(1-X)Sr_(X)MnO₃ ontemperature, reported in the past. As FIG. 2 indicates, the reflectivitynoticeably changes with changes in temperature around photon energy ofabout 0.12 eV (10 μm) which is the peak of heat radiation around roomtemperature. The phase transition temperature is variable between 250 Kand 350 K in accordance with the composition ratio x of La and Sr.

[0017]FIG. 3 shows data representative of the hemispherical reflectivityof La_(0.825)Sr_(0.175)MnO₃ and measured in the range of from 170 K to380 K. As shown, the reflectivity sharply changes in the range of from300 K to 280 K, i.e., at the phase transition temperatures. As a result,the above substance exhibits the characteristic of metal at the lowtemperature side, but exhibits the characteristic of an insulator at thehigh temperature side.

[0018]FIG. 4 shows data representative of the result of measurement ofresistivity. As shown, the resistivity changes by about four times as inFIG. 2.

[0019] In the heat control device of the present invention, thevariable-phase substance should only be arranged on heat radiationsurfaces in the farm of a film and is therefore space-saving and lightweight. Moreover, the device is highly reliable because it needs nomovable portions. When the device is mounted in a position getting thesunlight, a silicon plate transparent for thermal infrared rays, butopaque for the sunlight, may be positioned in front of thevariable-phase substance in order to minimize the sunlight absorption ofthe device.

[0020] For the variable-phase substance, use may be made of an oxide ofMn-containing perovskite represented by A_(1-X)B_(X)MnO₃ where A denotesat least one of La, Pr, Nd and Sm rare earth ions, and B denotes atleast one of Ca, Sr and Ba alkaline rare earth ions. Further, such asubstance may be implemented by an oxide of Cr-containing corundumvanadium, preferably (V_(1-X)Cr_(X))₂O₃.

[0021] Referring to FIG. 5, a first embodiment of the heat controldevice in accordance with the present invention will be described. Asshown, the device is implemented by a variable-phase substance 1 forcontrolling the temperature of a desired object 2. The substance 1exhibits the characteristic of metal in a high temperature phase, butexhibits the characteristic of an insulator in a low temperature phase.Also, the substance 1 radiates a great amount of heat in the hightemperature phase, but radiates a small amount of heat in a lowtemperature phase. The substance 1 is affixed to the object 2 by powdercoating, evaporation, crystalline adhesion or similar affixing means. Inthe Illustrative embodiment, the substance 1 is implemented byLa_(I-X)Sr_(X)MnO₃ belonging to a family of oxides of perovskite Mn.

[0022] Specifically, the object 2 is representative of the heatradiation wall of a spacecraft. The substance 1 is arranged on thesurface 3 of the wall 2 in the form of a several hundred micron thickfilm. The substance 1 is thermally coupled to the surface 3 andsubstantially the same in temperature as the wall 2.

[0023] In operation, when the temperature of the surface 3 rises andheats the substance above the phase transition temperature, then theheat radiation ratio of the substance increases. As a result, the amountof heat radiation to the outside environment increases and lowers thetemperature of the surface 3. Conversely, when the temperature of thesurface 3 drops and cools off the substance below the phase transitiontemperature, the heat radiation ratio of the substance 1 and thereforethe amount of heat radiation decreases, raising the temperature of thesurface 3. With this mechanism, the substance 1 automatically controlsthe temperature of the surface 3 to a range around its phase transitiontemperature.

[0024] The substance 1 has a cubic crystal structure and has an opticalproperty not dependent on the orientation of the crystallographic axis.It follows that the substance 1 can be arranged on the surface 3 by anyone of conventional schemes including powder coating, evaporation,crystal line adhesion and other affixing means and the adhesion of afilm implemented by a powdery phase-variable substance containing, e.g.,a binder.

[0025] The illustrative embodiment is practicable only if thevariable-phase substance is implemented by, e.g., an oxide ofMn-containing perovskite represented by A_(1-X)B_(X)MnO₃ where A denotesat least one of La, Pr, Nd and Sm rare earth ions, and B denotes atleast one of Ca, Sr and Ba alkaline rare earth ions. Further, such asubstance may be implemented by an oxide of Cr-containing corundumvanadium, preferably (V_(1-X)Cr_(X))₂O₂.

[0026] A second embodiment of the heat control device in accordance withthe present invention will be described with reference to FIG. 6. Asshown, the device is also implemented by the variable-phase substance 1for controlling the temperature of the object 2. The substance 1exhibits the characteristic of metal in a high temperature phase, butexhibits the characteristic of an insulator in a low temperature phase,as stated earlier. In addition, the substance 1 radiates a great amountof heat in the high temperature phase, but radiates a small amount ofheat in a low temperature phase, as also stated previously. In theillustrative embodiment, a silicon plate 4 transparent for infraredrays, but opaque for visible rays, is positioned an the substance 1.

[0027] As shown in FIG. 2, La_(1-X)Sr_(X)MnO₃ constituting the substance1 has reflectively as low as about 0.2 in the sunlight wavelength range(0.3 μm to 2.5 μm), i.e., it shows high absorbance to the sunlight insuch a range. Therefore, when the substance is positioned in an areadirectly getting the sunlight, its absorbance is increased to obstructheat radiation. In such a case, as shown in FIG. 6, the silicon plate 4transparent for infrared rays, but opaque for visible rays, is mountedon the front of the substance 1. This embodiment is therefore identicalin principle with the first embodiment except that the silicon plate 4reflects the sunlight.

[0028] If desired, the silicon plate 4 may be replaced with any othermember, e.g., a plate or a film containing germanium so long as it cantransmit infrared rays.

[0029] In summary, it will be seen that the present invention provides asmall size, light weight heat control device using an optical propertyparticular to a substance itself in place of a mechanical principleapplied to a conventional thermal louver. In addition, the device of thepresent invention is highly reliable and long life because it needs nomovable portions which would bring about wear, fatigue and otherproblems.

[0030] Various modifications will become possible for those skilled inthe art after receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

What is claimed is:
 1. In a heat control device, a variable-phasesubstance exhibiting a property of an insulator or a property of metalin a high temperature phase or a low temperature phase, respectively,and radiating a great amount of heat or a small amount of heat in thelow temperature phase or the high temperature phase, respectively,controls a temperature of an object.
 2. A heat control device as claimedin claim 1 , wherein said variable-phase substance comprise an oxide ofperovskite Mn.
 3. A heat control device as claimed in claim 2 , whereinthe oxide of perovskite Mn comprises an oxide of Mn-containingperovskite represented by A_(1-X)B_(X)MnO₃ where A is at least one ofLa, Pr, Nd and Sm rare earth ions, and B is at least one of Ca, Sr andBa alkaline rare earth ions.
 4. A heat control device as claimed inclaim 3 , wherein said variable-phase substance is affixed to the objectby powder coating, evaporation, crystalline adhesion or adhesion of afilm formed of a variable-phase substance containing a binder.
 5. A heatcontrol device as claimed in claim 4 , further comprising either one ofa plate and a film mounted on said phase-variable substance fortransmitting infrared rays and reflecting visible rays.
 6. A heatcontrol device as claimed in claim 5 , wherein the object compriseseither one of an artificial satellite and a spacecraft.
 7. A heatcontrol device as claimed in claim 1 , wherein the oxide of perovskiteMn comprises an oxide of Mn-containing perovskite represented byA_(1-X)B_(X)MnO₃ where A is at least one of La, Pr, Nd and Sm rare earthions, and B is at least one of Ca, Sr and Ba alkaline rare earth ions.8. A heat control device as claimed in claim 7 , wherein saidvariable-phase substance is affixed to the object by powder coating,evaporation, crystalline adhesion or adhesion of a film formed of avariable-phase substance containing a binder.
 9. A heat control deviceas claimed in claim 8 , further comprising either one of a plate and afilm mounted on said phase-variable substance for transmitting infraredrays and reflecting visible rays.
 10. A heat control device as claimedin claim 9 , wherein the object comprises either one of an artificialsatellite and a spacecraft.
 11. A heat control device as claimed inclaim 1 , wherein said variable-phase substance comprises an oxide ofCr-containing corundum vanadium.
 12. A heat control device as claimed inclaim 1 , wherein said variable-phase substance comprises(V_(1-X)Cr_(X))₂O₃.
 13. A heat control device as claimed in claim 12 ,wherein said variable-phase substance is affixed to the object by powdercoating, evaporation, crystalline adhesion or adhesion of a film formedof a variable-phase substance containing a binder.
 14. A heat controldevice as claimed in claim 13 , further comprising either one of a plateand a film mounted on said phase-variable substance for transmittinginfrared rays and reflecting visible rays.
 15. A heat control device asclaimed in claim 14 wherein the object comprises either one of anartificial satellite and a spacecraft.
 16. A heat control device asclaimed in claim 1 , wherein said variable-phase substance comprises(V_(1-X)Cr_(X))₂O₃.
 17. A heat control device as claimed in claim 16 ,wherein said variable-phase substance is affixed to the object by powdercoating, evaporation, crystalline adhesion or adhesion of a film formedof a variable-phase substance containing a binder.
 18. A heat controldevice as claimed in claim 17 , further comprising either one of a plateand a film mounted on said phase-variable substance for transmittinginfrared rays and reflecting visible rays.
 19. A heat control device asclaimed in claim 18 , wherein the object comprises either one of anartificial satellite and a spacecraft.
 20. A heat control device asclaimed in claim 1 , wherein said variable-phase substance is affixed tothe object by powder coating, evaporation, crystalline adhesion oradhesion of a film formed of a variable-phase substance containing abinder.
 21. A heat control device as claimed in claim 20 , furthercomprising either one of a plate and a film mounted on saidphase-variable substance for transmitting infrared rays and reflectingvisible rays.
 22. A heat control device as claimed in claim 21 , whereinthe object comprises either one of an artificial satellite and aspacecraft.
 23. A heat control device as claimed in claim 1 , furthercomprising either one of a plate and a film mounted on saidphase-variable substance for transmitting infrared rays and reflectingvisible rays.
 24. A heat control device as claimed in claim 23 , whereinthe object comprises either one of an artificial satellite and aspacecraft.
 25. A heat control device as claimed in claim 23 , whereinthe object comprises either one of an artificial satellite and aspacecraft.
 26. In a method of controlling a temperature of an object, avariable-phase substance exhibiting a property of an insulator or aproperty of metal in a high temperature phase or a low temperaturephase, respectively, and radiating a great amount of heat or a smallamount of heat in the low temperature phase or the high temperaturephase, respectively, is affixed to said object.
 27. A method as claimedin claim 26 , wherein the object comprises either one of an artificialsatellite and a spacecraft.
 28. A method as claimed in claim 26 ,wherein said variable-phase substance comprises either one of an oxideof perovskite Mn and an oxide of Cr-containing corundum vanadium.
 29. Amethod as claimed in claim 28 , wherein the object comprises either oneof an artificial satellite and a spacecraft.